A number of cyanine dyes have been shown to produce photo-electric effects in artificial, membranes, which result from physical movement of charged dye molecules following light absorption. These photo-effects are conveniently observed as variations in the transmembrane voltage following a brief light pulse. The waveforms of these photo-effects in artificial membranes depend upon the type of membrane lipid, the salt concentration of the aqueous solution, and the temperature, as well as the particular dye structure. Since these factors determine the structure and intermolecular organization of the membranes, these wave form variations provide a method of detecting subtile variations in membrane structure. The work proposed in this research project is to systematically develop knowledge of this phenomena in artificial membranes, and to apply selected photo-electric membrane probes to biological cells to study the structure and intermolecular organization of cell membranes.